The packaging of electrical circuits is a key element in the technological development of any device containing electrical components. Integrated circuit (IC) chips are enclosed in plastic packages that enable electrical connection of the chip to other circuits. Packaging IC chips has involved the placement of a chip on a flexible board where following adhesion of the chip to the board and wire bonding to connect the leads from the chip to the terminals on the board, an encapsulant is flowed over the chip and board to form a sealed package.
Developments in semiconductor fabrication processes provides for integration of large numbers of transistors, diodes, and other circuit elements onto a single IC chip. Such IC chips generally require a large number of electrical connections to receive inputs and to supply outputs. Because these integrated circuits are generally very small, the required input/output electrical connections on the integrated circuit are both numerous and densely spaced.
Several technologies have been developed to provide a means of mounting these electrical connections on a surface of a substrate, such as a printed circuit board (PCB). One method of packaging integrated circuits for electrical connection to a PCB is the so-called ball grid array (BGA) package.
A BGA semiconductor package generally includes a semiconductor chip (an integrated circuit) mounted on the top surface of a substrate. Electrical connections are made from the die to the substrate with bond wires that are attached to bond pads provided on the die and the substrate. The bond pads on the substrate are electrically connected to an array of solder balls or bumps, and these solder balls are used to bond and as input/output terminals for electrically connecting the substrate to a PCB or other external device.
A drawback of conventional BGA packaging is the limited space available for attachment of solder balls for connection to an external device. Another drawback is that the package is longer than the chip in both the X and Y directions (i.e., width and length).